A wide variety of optoelectronic devices are known for emitting light and which may be used in various devices such as calculator displays, flat screen television screens and many other applications. Among various well known existing devices are light emitting diodes (LEDs), laser diodes, liquid crystals and electroluminescent devices.
A light emitting diode is a semiconductor device, in particular it is a p-n junction diode, that emits light as a result of direct radiative recombination of excess electron-hole pairs. In a semiconductor such as GaAs a significant amount of light can be emitted following injection of excess minority carriers. The useful light obtainable from such a device is dependent on various factors including the optical quality of the crystal surfaces. The colour of the light emitted is a property of the material used as the semiconductor since the energy of the emitted light is determined by the band-gap energy. Such devices are advantageous in that they can be made very small and if desired can be formed as part of an integrated circuit using convention circuit fabrication technologies. A disadvantage however is that the range of colours available from such devices are limited by the number of suitable materials available. The majority of suitable semiconductors, such as GaAs, emit useful light only in the red end of the spectrum.
Another known optoelectronic method of generating light is by utilising the property of electroluminescence. This is the emission of light by certain phosphorescent materials under the influence of an applied electric field. Again, however, with known materials there are problems with constructing a device that emits light at shorter wavelengths toward the blue end of the spectrum. This problem is compounded when attempting to find such a material that will emit blue light and which can be integrated into a circuit directly.